1. Field of the Invention
Embodiments disclosed herein generally relate to a system used to power and support equipment downhole. More particularly, embodiments disclosed herein relate to a system that includes a cable capable of powering and supporting, as well as raising and lowering, equipment downhole, such as a downhole pump.
2. Background Art
In the oil and gas industry, a wide variety of systems are known for producing fluids from a subterranean formation. Oil wells typically rely on natural gas pressure to propel crude oil to the surface. In formations providing sufficient pressure to force the fluids to the surface of the earth, the fluids may be collected and processed without the use of artificial lifting systems. Oftentimes, particularly in more mature oilfields that have diminished gas pressure or in wells with heavy oil, this pressure is not sufficient to bring the oil out of the well. In these instances, the oil can be pumped out of the wells using a pumping system.
Different types of pumping systems may be disposed downhole with a well to pump the desired fluids to the surface of the earth. For example, sucker rod pumps have been previously used to pump oil to the surface in low pressure wells. More recently, though, sucker rod pumps have been replaced with electrical submersible pumps (ESPs), such as a Russian Electrical Dynamo of Arutunoff (REDA) pump, which is commercially available from Schlumberger. A submersible pump is usually deposited within the production fluids to then pump the desired fluids to the earth's surface. As such, an electrical submersible pump typically includes a motor section, a pump section, and a motor protector to seal the clean motor oil from well fluids, in which the pump is deployed in a well and receives power via an electrical cable. These pumps are typically attached to the bottom of the production string and pump oil up from the bottom of the well by generating a pressure boost sufficient to lift production fluids even in deep water subsea developments. Power to these electrical submersible pumps is typically provided by “permanent” cables designed for long-term deployment in the well.
A typical submersible pumping system includes several components, such as a submersible electric motor that supplies energy to a submersible pump, and typically some kind of connector for connecting the submersible pumping system to a deployment system. Conventional deployment systems often include production tubing, cable, and/or coiled tubing. Additionally, power is supplied to the submersible electric motor via a power cable that runs through or along the deployment system.
Multiple different types of methods may be used to deploy these types of submersible pumping systems to pump up oil from a well. One basic deployment method involves attaching a submersible pump to the bottom of the production string and then pumping oil up the production string from a selected location within the well. Power is provided to the submersible pump by a “permanent” cable that is strapped to the production string and designed for long-term deployment in the well.
For example, with reference to FIG. 1, a submersible pumping system is shown that includes a submersible pump 110 attached to a pipe string 112. The submersible pump 110 is deployed in a well 114 and includes a permanent cable 116 that terminates at the well head 118. The permanent cable 116 is used to provide power to the submersible pump 110, but typically is not capable of actually suspending or supporting the submersible pump 110 in the well 114. Rather, the submersible pump 110 is attached to the pipe string 112, as the pipe string 112 supports the submersible pump 110 in the well 114, and the permanent cable 116 is then typically fixed to the pipe string 112 with metal straps (not shown). After attaching the cable 116 to the pipe string 112, the cable 116 is then cut at the well head 118 to the exact length needed to power the submersible pump 110 downhole. Once the permanent cable 116 is cut, both the submersible pump 110 and the cable 116 become a permanent fixture with the pipe string 112 in the well 114, as the entire pipe string 112 must be pulled out of the well 114 to remove the submersible pump 110 from the well 114.
Another basic deployment method for submersible pumping systems involves attaching a submersible pump to coiled tubing and running the coiled tubing down the center of the pipe string. Power is provided to the submersible pump by a power cable that is run through the center of the coiled tubing, and oil is then pumped by the submersible pump back up the pipe string. For example, with reference to FIG. 2, a deployment system is shown that includes coiled tubing 220 and coiled tubing grippers 222. The coiled tubing 220 includes a power cable disposed therein, in which the power cable normally must be injected into the coiled tubing 220, usually offsite, and then have the coiled tubing 220, along with the deployment equipment, transported to the well. To assist in deploying the coiled tubing 220, along with the submersible pump attached at an end thereof downhole, the coiled tubing grippers 222 may grip and engage the coiled tubing 220. As such, the coiled tubing grippers 222 may be powered and/or otherwise driven, such as include a chain-driven traction winch. Once the submersible pump is at the desired location, the coiled tubing 220, along with the power cable disposed inside, are cut at the well head and left in place within the well.
Further, another basic deployment method for submersible pumping systems involves a two cable method commonly referred to as a cable deployed pumping system (CDPS). This method involves lowering and suspending a submersible pump within the pipe string from a wire-rope cable with a second, non-supporting, electrical cable providing power to the pump. For example, with reference to FIG. 3, a deployment system is shown that includes a support cable 330 and a power cable 332. The support cable 330 normally is a torque-balanced wire rope support cable that is tied and/or banded together with the power cable 332 at frequent intervals as the submersible pump, attached to the ends of the support cable 330 and the power cable 332, is deployed into the well 334. Banding to keep the cables 330 and 332 together is applied by personnel at the well head 336 as the cables 330 and 332 are passed into the well 334.
After the submersible pump at the ends of the cables 330 and 332 is lowered to the desired location, the support cable 330 is attached to a hanger packoff (not shown) at the well head 336. Particularly, the support cable 330 is often attached to a polished “pony rod” that is connected to the hanger packoff using multiple splice rods, such as splice rods available from PMI Industries, Inc. The splice rods are multiple loosely coiled, steel rods that wrap around and grip the end of the polished pony rod, as well as grip the end of the wire rope support cable 330, as the ends of the pony rod and the support cable 330 butt up against each other. As such, the splice rods are designed to tighten the grip with the pony rod and support cable 330 as the tension between the pony rod and support cable 330 increases. The submersible pump is then secured in a landing seat in a packer (not shown) located at a selected location within the well 334. Once secured, the submersible pump is used to pump oil up through the well 334, such as through a pipe or production string within the well 334.
Problems may exist, however, with each of these different types of deployment methods and systems. For example, because the power cables used to power the submersible pumps are typically not strong enough to support the weight of the submersible pumping system downhole, the submersible pumping system must be provided with additional support (e.g., equipment) in the well. However, deploying the submersible pump 110 using the pipe string 112 in FIG. 1 can be an extremely labor-intensive and time-consuming process, as a workover rig is required to feed the pipe string 110 into the well 114, and the power cable 116 must be pneumatically banded at regular intervals to the outside of the pipe string 112. Further, in the event that problems occur with the submersible pump 110 after deployment, the entire process must be reversed and repeated, thereby removing the pipe string 112 section-by-section as the banding is removed and starting over.
Additionally, using the coiled tubing 220 in FIG. 2 to deploy a submersible pump downhole requires the tedious process of first injecting a power cable into the coiled tubing, then transporting the bulky, heavy reel of coiled tubing and the associated deployment equipment to the wellsite. This method also requires using customized lengths of expensive coiled tubing, as the coiled tubing must be cut and left in place in the well during pumping.
Further, with reference to FIG. 3, applying banding to the cables 330 and 332 as the cables 330 and 332 are passed down into the well 334 may create a safety hazard for the personnel applying the banding. The desire to advance the cables 330 and 332 quickly into the well tends to increase the safety risk, and the bands applied to the cables 330 and 332 tend to slip as the cables 330 and 332 are slacked and tightened, leading to potential twisting and bunching downhole. Furthermore, as with the pipe string and coiled tubing methods, if any problems are encountered during the deployment of the pump, a significant delay will be experienced as the process of retrieving the pump, correcting the issue, and redeploying will be extremely slow. Further, the power cable is not designed to withstand the stresses, pressures, and fluid infiltration that are typically encountered downhole as the oil is pumped uphole around the power cable. Accordingly, there exists a need for a system that may be deployed and retracted from the well independently from the pipe string and that is capable of withstanding the extreme downhole environment.